1. Field of the Invention
The present invention relates to a towing device for an electric vehicle, for towing an electric vehicle, which employs only an electric motor as a drive source, using a towing vehicle when the electric vehicle becomes unable to travel under its own power.
2. Description of the Related Art
In recent years, electric vehicles employing only an electric motor as a drive source have come to public attention amid concerns about preventing atmospheric pollution and reducing vehicle noise. When an electric vehicle becomes unable to travel under its own power due to a breakdown, a different response to that of a vehicle having an internal combustion engine is required. When a vehicle having an internal combustion engine breaks down and the cause of the breakdown is insufficient battery charge, a starter motor can be jump-started using a battery from another vehicle. Hence, depending on the cause of the breakdown, emergency measures can be taken on the spot. When emergency measures cannot be taken, the vehicle can be towed away easily using a towing vehicle.
When an electric vehicle becomes unable to travel under its own power, on the other hand, not only is time required to charge a high voltage battery used to drive the motor, but also, a diagnosis must be made as to whether the breakdown has occurred in a drive system or a control system, which are constituted by electric devices and control devices, and therefore the broken-down vehicle must be placed on a carrier car or towed by a towing vehicle and transported to a repair plant. However, depending on the cause of the breakdown, it may not be desirable to tow a vehicle that cannot travel under its own power due to a breakdown using a towing vehicle. In the case of an electric vehicle, a drive motor for driving vehicle wheels is driven to rotate by the tires when the vehicle is towed, and when the drive motor rotates, counter electromotive force is generated. Depending on the cause of the breakdown, a high voltage may be supplied to an electronic device of the control system as a result, causing damage to the electronic device. Japanese Unexamined Patent Application Publication 2002-233003 describes a power supply device for an electric vehicle having a plurality of batteries, in which power supply to a motor is prevented when a battery breaks.
As noted above, an electric vehicle may break down due to breakage of the various driving devices constituting the drive system or breakage of the various electronic devices constituting the control system, and depending on the cause of the breakdown, an electronic device of the control system may become damaged when the broken-down vehicle is towed. Therefore, the broken-down vehicle is transported to a repair plant on a specialized carrier car, rather than being towed by a towing vehicle. However, depending on the cause of the breakdown, it is possible in many cases to tow the broken-down vehicle without damaging the electronic devices, and in such cases transportation by carrier car is not necessary. By providing a clutch in the drive system of the electric vehicle and ensuring that the clutch is released during towing, the electric motor can be prevented from rotating during towing, and as a result, the generation of counter electromotive force from the electric motor during towing can be prevented. Thus, the electric vehicle can be towed regardless of the type of breakdown. However, a large amount of space must be secured in the drive system to install a towing clutch in the drive system.